The Greenhouse Gas Bulletin showed that concentrations of carbon dioxide (globally averaged) reached 407.8 parts per million in 2018, up from 405.5 parts per million (ppm) in 2017. The increase in CO2 from 2017 to 2018 was very close to that observed from 2016 to 2017 and just above the average over the last decade. What is important to know is that global levels of CO2 crossed the symbolic and significant 400 parts per million benchmark in 2015.
Note that ‘emissions’ represent what goes into the atmosphere, and ‘concentrations’ represent what remains in the atmosphere after the complex system of interactions between the atmosphere, biosphere, lithosphere, cryosphere, and the oceans. About a quarter of the total emissions is absorbed by the oceans and another quarter by the biosphere.
Also reported is that concentrations of methane and nitrous oxide surged by higher amounts than during the past decade, according to observations from the Global Atmosphere Watch network.
In summary, the report states that since 1990, there has been a 43% increase in the warming effect on the climate – labelled ‘total radiative forcing’ – by long-lived greenhouse gases. CO2 accounts for about 80% of this, since CO2 remains in the atmosphere for centuries, and in the oceans for even longer.
The WMO Secretary-General explains that the last time the Earth experienced a comparable concentration of CO2 was 3-5 million years ago. Back then, the temperature was 2-3°C warmer, and the sea level was 10-20 metres higher than now.